A Soyuz capsule carrying three astronauts touched down to Earth early today after undocking from the International Space Station following 166 days in space.

American Chris Cassidy and Russians Pavel Vinogradov and Alexander Misurkin emerged from the capsule in smiles on an unusually sunny day in Kazakhstan.

Live coverage from Nasa, the US space agency, first showed the shuttle parachuting to a safe and punctual landing. Helicopters were then flown to the landing site, where medical and flight crews helped the three men disembark.

The capsule undocked from the space station for a flight to Earth that took just over three hours. The three men blasted off from the Baikonur cosmodrome on March 29.

Each of the men was carried to reclining chairs, where they spent several minutes in order to acclimatize to Earth's gravity.

A Nasa TV commentator said that crew members Misurkin and Cassidy would be taken to a medical center, where they will undergo various tests that could provide information for future flights. Vinogradov, at 60 the oldest human ever to land in a Soyuz vehicle, would not take part in the same experiments.

Currently the Russian Fyodor Yurchikhin, Karen Nyberg of Nasa and the Italian Luca Parmitano are tending the International Space Station until the arrival of a three-person crew scheduled to launch from Kazakhstan on September 25.

The Soyuz is the only means for international astronauts to reach the orbiting laboratory since the decommissioning of the US shuttle fleet in 2011.